The free radical (catalyzed) polymerization of perfluorovinyl monomers to perfluorinated polymers (both plastics and elastomers) is a well known process, see for instance U.S. Pat. Nos. 3,132,123, 3,467,638, 3,682,872, 4,948,853, 4,973,634, and 4,983,697, and H. Mark., et al., Ed., Encyclopedia of Polymer Science and Engineering, 2nd. Ed., Vol. 16, John Wiley & Sons, New York, 1989, p. 577-648, which are all hereby included by reference. In such a polymerization the monomer(s) is (are) contacted with a free radical initiator and the polymerization is allowed to proceed. Such polymerizations are often carried out in solution, aqueous suspension or emulsion, or by other means. Perfluorinated plastics are useful in many applications wherein high temperature resistance and/or good chemical resistance are important. Perfluoroelastomers are useful in similar applications wherein elastomeric properties are desired, as in various types of seals such as brings, chevron rings, shaft seals, and valve packing and washers.
In making these polymers for various applications it is often desirable to control the molecular weight, particularly to decrease the- molecular weight from that which would be obtained in the absence of chain transfer agents. Lower molecular weight polymers often are easier to process, i.e., form into useful shapes. If the polymer is to be crosslinked, it is preferred that any chain transfer agent that is used contain functional groups such that end groups of the polymers, which are mostly formed by a chain transfer reaction involving the chain transfer agent, contain functional groups which may act as crosslinking sites (sometimes also called curesites). By reacting the chain ends, crosslinked networks with better physical properties are often obtained.
One useful type of chain transfer agent in such polymerizations is fluorinated alkyl iodides, especially fluorinated alkyl diiodides. When an alkyl diiodide causes a chain transfer reaction to occur, both chain ends that form contain iodine, which may be used as a curesite to crosslink the polymer. However, these diiodides, and/or byproducts produced in their syntheses are often quite toxic, thereby requiring extra precautions (and expense) in their manufacture and use. Less toxic substitutes that perform the chain transfer function, and which provide curesites at chain ends, are therefore desirable. The use of such iodides as chain transfer agents is reported in U.S. Pat. Nos. 4,000,356, 4,243,770, 4,361,678, 4,948,852, 4,948,853, 4,973,633, 4,973,634, and 4,983,697. None of these patents describe the use of the chain transfer agents described herein.
A. V. Fokin, et al., Izy. Akad. Nauk. SSSR, Ser. Khim., vol. 35 (1985), p. 2298-2302, describe the preparation of .beta.-haloperfluoroethane fluorosulfates in relatively low yield by the reaction of tetrafluoroethylene, a halogen, and fluorosulfonic acid. The use of chlorosulfonic acid is not described in this references.
U.S. Pat. No. 4,835,305 describes the preparation of iodo- and bromo-substituted perfluoropropyl fluorosulfates by the reaction of bromo- or iodofluorosulfonic acid and hexafluoropropene.